Fuel Injectors, Gasoline Direct Injection

Overview 

The Gasoline Direct Injection (GDI) system is similar to a Port Fuel Injection (PFI) system with the exception of an added high-pressure pump.

• An in-tank pump supplies 65 psi fuel to the high pressure, camshaft-driven pump.
• The PCM-controlled pump produces a selectable pressure in the fuel rail(s).
• On/off injectors meter the high pressure fuel directly into the cylinders.

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Gasoline Direct Injection (GDI) injectors spray liquid fuel, under high pressure, directly in the cylinder when activated. The high pressure fuel is supplied to the injector by a common fuel rail. The desired fuel pressure is determined by the PCM. Fuel injector pulse width is based on actual fuel pressure which is measured by a pressure sensor in the common rail.

Injection typically occurs in the cylinder's intake and compression stroke. Under certain conditions, multiple injections can occur per cylinder event. Since injection pressure is variable, the fuel mass injected is a function of both fuel pressure and injector pulse width.

A typical PFI injector is activated by applying battery voltage to it. The GDI injector driver applies a high voltage (65 volts) to initially open the injector and then controls injector current to hold it open during injection.

Fuel Injectors 

A typical PFI injector is single side controlled by the PCM. The GDI injector has two wires per injector routed to the PCM. The injector high side goes to a PCM pin (or two pins) that are common between an injector pair. The PCM contains a smart driver that monitors and compares high side and low side injector currents to diagnose numerous faults. All injector fault modes, however, are mapped into a single DTC per injector.

A higher-than-battery-voltage supply (internally generated within the PCM) is used to open the injector and modulated battery voltage holds the injector open. The injector driver IC controls three transistor switches that apply the boost voltage and then modulate injector current. Should that full voltage be unavailable, the proper injector opening current may not be generated in the time required. This fault (P062D) is detected on a per cylinder basis and reported without specifying a particular cylinder.